Caption: Telegraphone, early 20th-century artwork. This sound-recording device was invented in 1898 by the Danish engineer Valdemar Poulsen (1869-1942). It demonstrated the principle of magnetic recording and could be used to record and play back sounds. Here, the recording medium was a magnetic wire. It was not until later that magnetic tape was used as the recording medium. The wire is seen moving between two coils, past a recording or playback head. The combined telephone microphone and earpiece is at lower left. Artwork from the 26th volume (second period of 1900) of the French popular science weekly 'La Science Illustree'.